This invention relates to an electromechanical actuator and, in particular, to an electromechanical actuator that is ideally suited for use in controlling the positioning of a valve.
More specifically, this invention involves an extremely compact electromechanical actuator. Actuators are well known in the art and are used in many applications where a reciprocating linear motion is needed for some intended purpose. These hydraulic or pneumatic devices, as well as electrically powered devices, and to some extent pneumatic actuators, are capable of being contained in compact packages, while at the same time being capable of delivering relatively high forces. These devices, however, develop leaks which render them unreliable or inoperative over a period of time.
Electrically powered devices are generally referred to as electromechanical actuators and have proven to be more reliable than the hydraulic and pneumatic devices and exhibit a relatively longer life. In addition, the electrical power devices afford greater control over the positioning of the device. The electrically powered devices, however, consume more space than their hydraulic and pneumatic counterparts. Heat disruption is sometimes a problem with the electrical devices, particularly when attempting to compact the actuator in a small package.
It is, therefore, a primary object of the present invention to improve linear actuators and, in particular, to improve electromechanical linear actuators.
A further object of the present invention is to provide a compact electromechanical linear actuator that is capable of delivering a relatively high linear force at high speed.
A still further object of the present invention is to provide an electromechanical linear actuator having improved control capabilities and a high force vs. stroke characteristic.
Another object of the present invention is to provide a compact electromechanical linear actuator that efficiently conducts motor generated heat to the surrounding ambient.
These and other objects of the present invention are attained by an electromechanical linear actuator that includes a hollow shaft and a brushless servo motor that is contained within a compact housing. The motor includes a stator containing the motor windings that is secured to an inner wall of the housing by a tapered wedge fabricated of a material having a high coefficient of thermal conductivity. The housing is provided with fins that surround the motor for dissipating heat efficiently into the immediate ambient. Springs are employed to hold the wedge supporting the motor stator in place to prevent displacement of the stator over a broad change in temperature. A rotor assembly is contained within the housing and includes an extended ball screw shaft that is aligned along the axis of the motor and coacts with a ball screw nut to position a push rod. The push rod and ball screw nut are linked to a linear guideway for directing the push rod along a linear path of travel.